// Tencent is pleased to support the open source community by making RapidJSON available.
//
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

// This is a C++ header-only implementation of Grisu2 algorithm from the publication:
// Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
// integers." ACM Sigplan Notices 45.6 (2010): 233-243.

#ifndef RAPIDJSON_DTOA_
#define RAPIDJSON_DTOA_

#include "diyfp.h"
#include "ieee754.h"
#include "itoa.h" // GetDigitsLut()

RAPIDJSON_NAMESPACE_BEGIN
namespace internal
{

#ifdef __GNUC__
    RAPIDJSON_DIAG_PUSH
    RAPIDJSON_DIAG_OFF(effc++)
    RAPIDJSON_DIAG_OFF(array - bounds) // some gcc versions generate wrong warnings
                                       // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
#endif

    inline void GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa,
                           uint64_t wp_w)
    {
        while (rest < wp_w && delta - rest >= ten_kappa &&
               (rest + ten_kappa < wp_w || /// closer
                wp_w - rest > rest + ten_kappa - wp_w))
        {
            buffer[len - 1]--;
            rest += ten_kappa;
        }
    }

    inline int CountDecimalDigit32(uint32_t n)
    {
        // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
        if (n < 10)
            return 1;
        if (n < 100)
            return 2;
        if (n < 1000)
            return 3;
        if (n < 10000)
            return 4;
        if (n < 100000)
            return 5;
        if (n < 1000000)
            return 6;
        if (n < 10000000)
            return 7;
        if (n < 100000000)
            return 8;
        // Will not reach 10 digits in DigitGen()
        // if (n < 1000000000) return 9;
        // return 10;
        return 9;
    }

    inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len,
                         int* K)
    {
        static const uint64_t kPow10[] = {1ULL,
                                          10ULL,
                                          100ULL,
                                          1000ULL,
                                          10000ULL,
                                          100000ULL,
                                          1000000ULL,
                                          10000000ULL,
                                          100000000ULL,
                                          1000000000ULL,
                                          10000000000ULL,
                                          100000000000ULL,
                                          1000000000000ULL,
                                          10000000000000ULL,
                                          100000000000000ULL,
                                          1000000000000000ULL,
                                          10000000000000000ULL,
                                          100000000000000000ULL,
                                          1000000000000000000ULL,
                                          10000000000000000000ULL};
        const DiyFp           one(uint64_t(1) << -Mp.e, Mp.e);
        const DiyFp           wp_w  = Mp - W;
        uint32_t              p1    = static_cast<uint32_t>(Mp.f >> -one.e);
        uint64_t              p2    = Mp.f & (one.f - 1);
        int                   kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
        *len                        = 0;

        while (kappa > 0)
        {
            uint32_t d = 0;
            switch (kappa)
            {
                case 9:
                    d = p1 / 100000000;
                    p1 %= 100000000;
                    break;
                case 8:
                    d = p1 / 10000000;
                    p1 %= 10000000;
                    break;
                case 7:
                    d = p1 / 1000000;
                    p1 %= 1000000;
                    break;
                case 6:
                    d = p1 / 100000;
                    p1 %= 100000;
                    break;
                case 5:
                    d = p1 / 10000;
                    p1 %= 10000;
                    break;
                case 4:
                    d = p1 / 1000;
                    p1 %= 1000;
                    break;
                case 3:
                    d = p1 / 100;
                    p1 %= 100;
                    break;
                case 2:
                    d = p1 / 10;
                    p1 %= 10;
                    break;
                case 1:
                    d  = p1;
                    p1 = 0;
                    break;
                default:;
            }
            if (d || *len)
                buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
            kappa--;
            uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
            if (tmp <= delta)
            {
                *K += kappa;
                GrisuRound(buffer, *len, delta, tmp, kPow10[kappa] << -one.e, wp_w.f);
                return;
            }
        }

        // kappa = 0
        for (;;)
        {
            p2 *= 10;
            delta *= 10;
            char d = static_cast<char>(p2 >> -one.e);
            if (d || *len)
                buffer[(*len)++] = static_cast<char>('0' + d);
            p2 &= one.f - 1;
            kappa--;
            if (p2 < delta)
            {
                *K += kappa;
                int index = -kappa;
                GrisuRound(buffer, *len, delta, p2, one.f,
                           wp_w.f * (index < 20 ? kPow10[index] : 0));
                return;
            }
        }
    }

    inline void Grisu2(double value, char* buffer, int* length, int* K)
    {
        const DiyFp v(value);
        DiyFp       w_m, w_p;
        v.NormalizedBoundaries(&w_m, &w_p);

        const DiyFp c_mk = GetCachedPower(w_p.e, K);
        const DiyFp W    = v.Normalize() * c_mk;
        DiyFp       Wp   = w_p * c_mk;
        DiyFp       Wm   = w_m * c_mk;
        Wm.f++;
        Wp.f--;
        DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
    }

    inline char* WriteExponent(int K, char* buffer)
    {
        if (K < 0)
        {
            *buffer++ = '-';
            K         = -K;
        }

        if (K >= 100)
        {
            *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
            K %= 100;
            const char* d = GetDigitsLut() + K * 2;
            *buffer++     = d[0];
            *buffer++     = d[1];
        }
        else if (K >= 10)
        {
            const char* d = GetDigitsLut() + K * 2;
            *buffer++     = d[0];
            *buffer++     = d[1];
        }
        else
            *buffer++ = static_cast<char>('0' + static_cast<char>(K));

        return buffer;
    }

    inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces)
    {
        const int kk = length + k; // 10^(kk-1) <= v < 10^kk

        if (0 <= k && kk <= 21)
        {
            // 1234e7 -> 12340000000
            for (int i = length; i < kk; i++)
                buffer[i] = '0';
            buffer[kk]     = '.';
            buffer[kk + 1] = '0';
            return &buffer[kk + 2];
        }
        else if (0 < kk && kk <= 21)
        {
            // 1234e-2 -> 12.34
            std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
            buffer[kk] = '.';
            if (0 > k + maxDecimalPlaces)
            {
                // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
                // Remove extra trailing zeros (at least one) after truncation.
                for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
                    if (buffer[i] != '0')
                        return &buffer[i + 1];
                return &buffer[kk + 2]; // Reserve one zero
            }
            else
                return &buffer[length + 1];
        }
        else if (-6 < kk && kk <= 0)
        {
            // 1234e-6 -> 0.001234
            const int offset = 2 - kk;
            std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
            buffer[0] = '0';
            buffer[1] = '.';
            for (int i = 2; i < offset; i++)
                buffer[i] = '0';
            if (length - kk > maxDecimalPlaces)
            {
                // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
                // Remove extra trailing zeros (at least one) after truncation.
                for (int i = maxDecimalPlaces + 1; i > 2; i--)
                    if (buffer[i] != '0')
                        return &buffer[i + 1];
                return &buffer[3]; // Reserve one zero
            }
            else
                return &buffer[length + offset];
        }
        else if (kk < -maxDecimalPlaces)
        {
            // Truncate to zero
            buffer[0] = '0';
            buffer[1] = '.';
            buffer[2] = '0';
            return &buffer[3];
        }
        else if (length == 1)
        {
            // 1e30
            buffer[1] = 'e';
            return WriteExponent(kk - 1, &buffer[2]);
        }
        else
        {
            // 1234e30 -> 1.234e33
            std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
            buffer[1]          = '.';
            buffer[length + 1] = 'e';
            return WriteExponent(kk - 1, &buffer[0 + length + 2]);
        }
    }

    inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324)
    {
        RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
        Double d(value);
        if (d.IsZero())
        {
            if (d.Sign())
                *buffer++ = '-'; // -0.0, Issue #289
            buffer[0] = '0';
            buffer[1] = '.';
            buffer[2] = '0';
            return &buffer[3];
        }
        else
        {
            if (value < 0)
            {
                *buffer++ = '-';
                value     = -value;
            }
            int length, K;
            Grisu2(value, buffer, &length, &K);
            return Prettify(buffer, length, K, maxDecimalPlaces);
        }
    }

#ifdef __GNUC__
    RAPIDJSON_DIAG_POP
#endif

} // namespace internal
RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_DTOA_
